Materials Science Lesson 5

3. Covalent Bonds Another way for atoms to fill their valence shell is through covalent bonding Covalent bonding occurs between a non-metal and a non-metal. Covalent bonding occurs when electrons are shared between two atoms.

3. Covalent Bonds Covalent bonds can occur as single, double or triple bonds Single bonds occur when one pair of electrons is shared between two atoms (each atom donating 1 electron to share) Double bonds occur when two pairs of electron are shared between two atoms (each atom donating two electrons to share) Triple bonds occur when three pairs of electrons are shared between two atoms (each atom donating three electrons to share)

3. Covalent Bonds You can predict the number of covalent bonds needed based on the number of valence electrons an atom contains. (remember electrons are negatively charged) Element Number of Valence e- e- needed to fill octet Possible bonds created Oxygen   Nitrogen Carbon

Molecules and Molecular Compounds A molecule is a neutral group of atoms joined together through covalent bonds. Noble gases have full valence shells naturally so they are the only monoaomic elements.

Molecules and Molecular Compounds There are 7 diatomic elements that occur in pairs in nature

Molecules and Molecular Compounds Determining the chemical formula of a molecule is more difficult than with an ionic compound because there can be many different compounds possible for the same two elements depending on the types of bonds that form. Unlike ionic compounds, covalent molecules molecular formula is not reduced to the lowest ratio. It represents the exact number of atoms that combine to form exactly one molecule.

Lewis Dot for the Formation or Molecular Compounds When given the chemical formula, you can use lewis dot structures to represent the bonding and show the structural formula for a molecule. Start by drawing out the lewis dot for each of the atoms involved. Then determine where the electrons will share in order for all atoms to bond together If you have a chemical formula where there is one atom of one element and several atoms of a different element, usually the element with one atom is in the middle surrounded by the others.

Ex: F2 Ex. HCN

Ex. NH3 Notice that an unshared pair can affect the shape of the molecule.

See Covalent Bonding Lewis Dot Assignment